Remove catback for drag racing on s/c car?

It might confuse the computer because the O2s won't get as good a reading.

90lxcoupe said:

you may loose boost from the loss of backpressure, when i switched to a 3" exhaust with the blower the car slowed down cause i went from 10psi to 8psi

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That doesn't make sense. Sounds like a tuning issue. Your 10psi has to do with restriction, it's all about CFM. It flowed better so it couldn't build as much pressure. Are you running a turbo? I just don't understand how backpressure in the exhaust coud effect a belt driven supercharger.

Cobra912 said:

Hmmm.......Now I'm confussed. I was always under the impression that even N/A cars benefited from a bit of back pressure, depending on the build of course. So should I see the same 6-7 lbs of boost, loose a little low end torque but gain up top?

I don't really wanna rip my exhaust off at the track tomorrow, but would be willing to try, just don't wanna waste my time if it makes no sense to do. It will probably be my last time this year and I'm aching for a low 11 time slip!!

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my 3" mufflers on my stock 94 Cobra killed my low end. I put the 2.5's on it and it was way better. My 347 in it was much happier with the 3's than the 2.5's and it made quite a bit of difference at the track.

Doing the exhaust at the track on back to back passes is the only way you'll really know if it does you any good. Otherwise it could be as simple as good or bad air on that night making the difference and not the exhaust.

90mustangGT said:

That doesn't make sense. Sounds like a tuning issue. Your 10psi has to do with restriction, it's all about CFM. It flowed better so it couldn't build as much pressure. Are you running a turbo? I just don't understand how backpressure in the exhaust coud effect a belt driven supercharger.

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It does and it doesent. The car should have run the same with slightly lower boost due to overall efficency. It prolly slowed down because now it was running too rich since I assume it was tuned for 10psi.

As for the pressure loss, it will happen on a turbo (with no EBC) or a supercharger. The cylinders can evacuate more exhaust with a less restrictive exhaust system. In return there is more volume to fill on the intake stroke causing there to be less pressure.
On a turbo that just has a spring on its waste gate it will be similar in PSI drop. Now if the turbos boost was controlled by an electronic boost controller then it would remain the same boost pressure cause the controller would keep the wastegate closed enough to reach the commanded boost level. If the turbo was at its limits though then that would also change the outcome.



Anyway, OP. Since you launch so high in the RPMs I would bet the car may be a tenth quicker with no exhaust. You may want to put a smaller pully on to keep the same boost level though so your fuel map stays inline and it does not run overly rich.

LaserSVT said:

It does and it doesent. The car should have run the same with slightly lower boost due to overall efficency. It prolly slowed down because now it was running too rich since I assume it was tuned for 10psi.

As for the pressure loss, it will happen on a turbo (with no EBC) or a supercharger. The cylinders can evacuate more exhaust with a less restrictive exhaust system. In return there is more volume to fill on the intake stroke causing there to be less pressure.
On a turbo that just has a spring on its waste gate it will be similar in PSI drop. Now if the turbos boost was controlled by an electronic boost controller then it would remain the same boost pressure cause the controller would keep the wastegate closed enough to reach the commanded boost level. If the turbo was at its limits though then that would also change the outcome.



Anyway, OP. Since you launch so high in the RPMs I would bet the car may be a tenth quicker with no exhaust. You may want to put a smaller pully on to keep the same boost level though so your fuel map stays inline and it does not run overly rich.

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What are we gonna do with you Laser? 4K high? You're not getting high till it tops 6500....and approaches 7K.

I ment as opposed to some people that launch at 2000 RPM.
Sorry, been hanging with the Mark VIII crowd too much and they all launch at idle-2200 RPM.

LaserSVT said:

I ment as opposed to some people that launch at 2000 RPM.
Sorry, been hanging with the Mark VIII crowd too much and they all launch at idle-2200 RPM.

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oh I understand now. Apparently I've been hanging around the guys at the drag strip too much.

It's never a good feeling when you notice your didn't remember to turn the launch limiter on when you're in the return road. It's then that you realize you just got done launching off the 7500 top end limiter. oops

I have never had anything with the ability to launch like that. I had an S4 but the most I ever pushed it at launch was 5000 RPM. It was under warrenty though.

I am envious of you guys and teh bad ass cars. Even when I do gears and Trac Lok and drag radials on my Mark the best i could ever do with a Stall would be 2500 on launch.

NikwoaC said:

It might confuse the computer because the O2s won't get as good a reading.

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the o2's are at the front of the H pipe. they will read the same. he is talking about undoing the mufflers from the h pipe

Maybe I missed it but whats your catback? If its decent you wont be gaining anything, longtubes and a x pipe will deff help.

Cobra912 said:

There is a member "The Bock" I believe who has the same blower on a notch with a 302 running 10.90's!

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what kind of suspension is he running? same engine?